In recent years, it has been seriously desired to reduce carbon dioxide emission in order to cope with air pollution and global warming. In the automobile industry for example, introduction of electric vehicles (EV), hybrid electric vehicles (HEV) and the like is expected to reduce carbon dioxide emission. For this reason, development of secondary cells for driving a motor, which is a key to a practical use of these vehicles, has been actively made.
Among secondary cells for driving a motor, lithium-ion secondary cells have drawn attention for the high theoretical energy, and the development thereof has been being made in a rapid pace. A typical lithium ion secondary cell includes a cathode that is formed by applying a cathode slurry containing a cathode active material on the surface of a current collector, an anode that is formed by applying an anode slurry containing an anode active material on an anode current collector, an electrolyte disposed between the cathode and the anode, and a cell case that houses the cathode, the anode and the electrolyte.
Selection of such active materials is of great importance in order to improve the capacity properties and the output properties of lithium-ion secondary cells.
For example, Patent Document 1 describes a proposal for improving the thermal stability of a non-aqueous electrolyte secondary cell that uses a lithium-containing transition metal oxide of a predetermined composition as a base material of the cathode active material, in which the cell is configured to have a counter charge capacity ratio between the anode and the cathode of 1.0 to 1.15 when it is charged until the potential of the cathode reaches 4.5 V.